Squelching Sierra fires left forest ready to burn

August 28, 2013 by Brian Skoloff in Earth / Environment

The Rim Fire burns through trees near Yosemite National Park, Calif., on Tuesday, Aug. 27, 2013. Firefighters gained some ground Tuesday against the huge wildfire burning forest lands in the western Sierra Nevada, including parts of Yosemite National Park. (AP Photo/Jae C. Hong)

Unnaturally long intervals between wildfires and years of drought primed the Sierra Nevada for the explosive conflagration burning the rugged landscape on the edge of Yosemite National Park, forestry experts say.

The fire had ravaged 288 square miles (745 sq. kilometers) by Tuesday night, making it the biggest fire in the Sierra's recorded history and one of the largest on record in California.

Containment held steady at 20 percent, but the number of destroyed structures rose to 111, and some 4,500 structures remained threatened. At least 31 residences were among those lost. Firefighters were making stands at Tuolumne City and other mountain communities.

Officials said they expected the blaze to continue to grow overnight.

"We're going to get a handle on it, but we're going to have to give some ground to get some," said Lee Bentley, fire spokesman for the U.S. Forest Service.

The blaze was just 40 acres (16 hectares) when it was discovered near a road in Stanislaus National Forest on Aug. 17, but firefighters had no chance of stopping it in the early days.

Fueled by thick forest floor vegetation in steep river canyons, it exploded to 105,620 acres (42,743 hectares) within the next two days. On its 11th day, it had surpassed 179,400 acres (72,602 hectares), becoming the seventh-largest California wildfire in records dating to 1932.

A tree burns near Yosemite National Park, Calif., on Tuesday, Aug. 27, 2013. Firefighters gained some ground Tuesday against the huge wildfire burning forest lands in the western Sierra Nevada, including parts of Yosemite National Park. (AP Photo/Jae C. Hong)

Federal forest ecologists say that historic policies of fire suppression to protect Sierra timber interests left a century's worth of fuel in the fire's path.

"That's called making the woodpile bigger," said Hugh Safford, an ecologist with the U.S. Forest Service in California.

A fire crew digs a fire line near Yosemite National Park in this photo made on Sunday, Aug. 25, 2013, and released by the US Forest Service on Tuesday. Firefighters continue to battle the Rim Fire, which has ravaged 282 square miles by Tuesday, the biggest in the Sierra's recorded history. (AP Photo/US Forest Service, Mike McMillan)

Two years of drought and a constant slow warming across the Sierra Nevada also worked to turn the Rim Fire into an inferno. For years forest ecologists have warned that Western wildfires will only get worse.

Sprinkler lines are set around the perimeter of a grove of giant sequoias in Yosemite National Park in this photo made on Sunday, Aug. 25, 2013, and released by the National Park Service on Tuesday. Yosemite crews continue to keep water on the Merced and Tuolumne groves of giant sequoias less than 10 miles from the front lines of the Rim Fire, which has ravaged 282 square miles by Tuesday, the biggest in the Sierra's recorded history. (AP Photo/National Park Service)

Sprinkler lines are set around the perimeter of a grove of giant sequoias in Yosemite National Park in this photo made on Sunday, Aug. 25, 2013, and released by the National Park Service on Tuesday. Yosemite crews continue to keep water on the Merced and Tuolumne groves of giant sequoias less than 10 miles from the front lines of the Rim Fire, which has ravaged 282 square miles by Tuesday, the biggest in the Sierra's recorded history. (AP Photo/National Park Service)

A helicopter dumps water on hot spots battling the Rim Fire in the Stanislaus National Forest along Highway 120 near Yosemite National Park, Monday, Aug. 26, 2013 in, Calif. With winds gusting to 25mph on Sierra, hundreds of firefighters have been deployed to protect this and other communities in the path of the Rim Fire raging north of Yosemite National Park. (AP Photo/The Sacramento Bee, Paul Kitagaki Jr.)

Paint peels after the sign was burned from the Rim Fire in the Stanislaus National Forest along Highway 120 near Yosemite National Park, Monday, Aug. 26, 2013 in, Calif. With winds gusting to 25mph on Sierra, hundreds of firefighters have been deployed to protect this and other communities in the path of the Rim Fire raging north of Yosemite National Park. (AP Photo/The Sacramento Bee, Paul Kitagaki Jr.)

In this Monday, Aug. 26, 2013 satellite photo released by NASA, a smoke plume trails north from the drought-fueled Rim Fire, center, burning near Yosemite National Park in central California. Red outlines indicate hot spots where the satellite detected unusually warm surface temperatures associated with fires. Containment of the fire more than doubled to 15 percent, although it was within a mile of the park's Hetch Hetchy Reservoir, the source of San Francisco's famously pure drinking water, officials said. (AP Photo/NASA)

Fire trucks drive through heavy smoke generated by the Rim Fire near Yosemite National Park, Calif., on Tuesday, Aug. 27, 2013. Firefighters gained some ground Tuesday against the huge wildfire burning forest lands in the western Sierra Nevada, including parts of Yosemite National Park. (AP Photo/Jae C. Hong)